Researchers have identified four key turning points in brain wiring at ages 9, 32, 66, and 83, based on MRI scans of nearly 3,800 people. These shifts could explain variations in learning capacity and risks for conditions like dementia. The findings highlight how brain connections evolve through five distinct phases over a lifetime.
A new analysis of brain scans suggests that human brain wiring experiences dramatic reorganizations at specific ages, potentially influencing cognitive abilities and disease risks. Led by Alexa Mousley at the University of Cambridge, the study examined MRI data from around 3,800 individuals in the UK and US, ranging from newborns to 90 years old. Participants were mostly white and excluded those with neurodegenerative or mental health conditions.
The research outlines five phases of brain development, marked by four turning points. From birth to age 9, white matter tracts—bundles of axons connecting brain regions—become longer and more convoluted, reducing efficiency. "It takes longer for information to pass between regions," Mousley explained. This phase may prioritize broad connections for learning, such as acquiring new skills, at the expense of speed, as unused links are pruned through experience.
Between ages 9 and 32, efficiency improves as connections shorten, allowing quicker information transfer. Mousley attributes this flip possibly to puberty's hormonal effects, supporting advancements in planning, decision-making, and working memory.
The longest phase, from 32 to 66, sees a gradual return to less efficient connections. "This phase is a point in your lifespan where your brain, of course, is still changing, but much less," Mousley noted. Factors like lifestyle shifts—such as parenthood or settling down—or general bodily wear might contribute, according to Mousley and Katya Rubia at King’s College London.
From 66 to 83, intra-regional connections stabilize more than inter-regional ones, coinciding with rising dementia risks. In the final phase, from 83 to 90, overall connections weaken, relying on central "hubs" for communication due to limited resources.
These patterns could clarify why mental health issues often emerge before age 25 and dementia risks increase after 65. "It’s important to understand the normal turning points in brain structure over the human lifespan, so we can, in future studies, explore what deviates during mental health or neurodegenerative conditions," Rubia said. Further research is needed on diverse populations to confirm the results.
The study appears in Nature Communications (DOI: 10.1038/s41467-025-65974-8).